The Federal Reserve also chipped in with more largesse in its emergency lending program for investment banks. The central bank announced late Sunday that it was broadening the types of collateral that financial institutions can use to obtain loans from the Fed.

Federal Reserve Chairman Ben Bernanke said the discussions had been aimed at identifying "potential market vulnerabilities in the wake of an unwinding of a major financial institution and to consider appropriate official sector and private sector responses."

The European Central Bank, the Bank of England, and the Swiss central bank also made more short-term credit available to banks. European stocks fell sharply, with the FTSE 100 Index off 3.42 percent in London, the CAC-40 down 4.27 percent in Paris, and Germany's blue-chip DAX 30 falling 3.38 percent. Asian stock markets also tumbled, with India's Sensex sinking more than 5 percent. Japan and Hong Kong were closed for holidays.

Financial stocks were hard hit and the dollar fell against the pound and the euro.

Futures pegged to the Dow Jones industrial average fell more than 250 points in electronic trading Sunday evening, pointing to a sharply lower open for the blue chip index Monday morning. Asian stock markets also tumbled, with India's Sensex sinking more than 5 percent. Japan and Hong Kong were closed for holidays.

The stunning weekend developments took place as voters, who rank the economy as their top concern, prepare to elect a new president in seven weeks. It likely will spur a much greater focus by presidential candidates — Republican John McCain and Democrat Barack Obama — and members of Congress on the need for stricter financial regulation.

Samuel Hayes, finance professor emeritus at Harvard Business School, said the Bush administration may get a lot of blame for the situation, which could benefit Obama.

"Just the psychological impact of this kind of failure is going to be significant," he said. "It will color people's feelings about their well-being and the integrity of the financial system."

Lehman Brothers' announcement that it is filing for bankruptcy came after all potential buyers walked away. Potential suitors were spooked by the U.S. Treasury's refusal to provide any takeover aid, as it had done six months ago when Bear Stearns faltered and earlier this month when it seized Fannie Mae and Freddie Mac.

Employees emerging from Lehman's headquarters near the heart of Times Square Sunday night carried boxes, tote bags and duffel bags, rolling suitcases, framed artwork and spare umbrellas. Many were emblazoned with the Lehman Brothers name. Its businesses in Britain were placed in administration Monday, said the administrator, accounting firm PricewaterhouseCoopers, and employees carrying boxes and bags were walking out of Lehman's London offices.

TV trucks lined Seventh Avenue opposite the building, while barricades at the building's main entrance attempted to keep workers and onlookers from gumming up the steady flow of pedestrians flowing in and out of Times Square.

Some workers had moist eyes while a few others wept and shared hugs. Most who left the building quietly declined interviews.

People snapped pictures with cameras and their phones. Observers pressed up against a police barricade drew the ire of one man who emerged from the building and shouted: "Are you enjoying watching this? You think this is funny?"

Merrill Lynch, another investment bank laid low by the crisis that was triggered by rising mortgage defaults and plunging home values in the U.S., agreed to be acquired by Bank of America for 0.8595 shares of Bank of America common stock for each Merrill Lynch common share.

That values Merrill at $29 a share, a 70 percent premium over the brokerage's Friday closing price of $17.05, but well below what Merrill was worth at its peak in early 2007, when its shares traded above $98.

Charlotte, N.C.,-based Bank of America has the most deposits of any U.S. bank, while Merrill Lynch is the world's largest brokerage. A combination of the two would create a global financial giant to rival Citigroup Inc., the biggest U.S. bank in terms of assets.

Strategically, most industry analysts say it's a good fit. If the deal goes according to plan, Bank of America will be able to offer Merrill's retail brokerage services to its huge customer base. There is not a great deal of overlap between the two companies — Bank of America does have an investment bank already, but it has never been terribly strong.

Where there is duplication, however, the combination of the two companies could result in more layoffs. Both Merrill and Bank of America have already cut thousands of investment banking jobs over the past year.

The deal would not come without risks, however. Merrill Lynch, like many of its Wall Street peers, has been struggling with tight credit markets and billions of dollars in assets tied to mortgages that have plunged in value. Merrill has reported four straight quarterly losses.

Bank of America's own finances are far from robust. As consumer credit deteriorates, the bank has seen its profits decline, and the company is still in the midst of absorbing the embattled mortgage lender Countrywide Financial, which it acquired in January.

Insurer AIG, hit hard by deterioration in the credit markets, said Sunday it is reviewing its operations and discussing possible options with outside parties to improve its business after a week when its stock dropped 45 percent amid concerns about the company's financial underpinnings.

The Wall Street Journal and The New York Times both reported early Monday on their Web sites that the American International Group is seeking an additional $40 billion in emergency funds — possibly from the Federal Reserve — to help it avoid a credit rating downgrade, which would make it more expensive for AIG to raise money. The insurer has already raised $20 billion in fresh capital this year.

AIG was working with New York Insurance Superintendent Eric Dinallo and a representative of the governor's office through the weekend to craft a solution that protects policyholders, according to Dinallo's spokesman David Neustadt.

"It's clear we're one step away from a financial meltdown," said Nouriel Roubini, chairman of the consulting firm RGE Monitor.

The meetings that began Friday night were a who's who of financial heavyweights: Treasury Secretary Hank Paulson, Timothy Geithner, president of the New York Fed, Securities and Exchange Commission Chairman Christopher Cox, and a host of CEOs, including Vikram Pandit of Citigroup Inc., Jamie Dimon of JPMorgan Chase & Co., John Mack of Morgan Stanley, Lloyd Blankfein of Goldman Sachs Group Inc., and Merrill Lynch & Co.'s John Thain.

For all their efforts, Lehman had to file for bankruptcy.

The end of Lehman may not stop the financial crisis that has gripped Wall Street for months, analysts said. More investment banks could disappear soon.

The independent broker-dealers "are going the way of the dodo bird," said Bert Ely, an Alexandria, Va.,-based banking consultant.

That's partly because some of the firms, particularly Merrill, made bad bets on real estate. But several analysts said that investment companies will need the deep pockets of commercial banks to survive the next few years.

On Sunday, there was also an emergency trading session being held at the International Swaps and Derivatives Association to "reduce risk associated with a potential Lehman Brothers Holdings Inc. bankruptcy." The ISDA, which arranges trades for derivatives, said it was allowing customers to make trades and unwind positions linked to Lehman.

Roubini said it's difficult to accurately gauge the health of companies like Merrill because their financial health depends on how they value complex securities. As a result, their finances aren't very transparent, he said.

That can lead to a loss of confidence in the financial markets, he said, which can overwhelm an investment bank even if it is financially healthy by some measures.

"Once you lose confidence, the fundamentals matter less," he said.

The common denominator of the financial crisis, analysts said, is the bursting of the housing bubble. Home prices have dropped on average 25 percent so far. Roubini predicted they could drop another 15 percent.

The crisis has begun to slow the broader economy as banks make fewer loans and consumers have begun cutting spending. Many economists are now forecasting that the economy could slip into recession by the end of this year and early next year.

The Fed is widely expected to keep interest rates steady at 2 percent, below inflation, when it meets Tuesday. It was possible, however, that the central bank might decide in coming weeks to cut rates if such a move is seen as needed to calm turbulent financial markets.

The International Monetary Fund predicted earlier this year that total losses from the credit crisis could reach almost $1 trillion. So far, banks have only taken about $350 billion in losses.

Commercial banks are also starting to feel the pinch. Eleven have closed so far this year, including Pasadena, Calif.-based IndyMac Bank, which had $32 billion in assets and $19 billion in deposits.

Christopher Whalen, managing director of Institutional Risk Analytics, a research firm, predicts that approximately 110 banks with $850 billion in assets could close by next July. That's out of 8,400 federally insured institutions, he said, which together hold $13 trillion in assets.

Individual customers are starting to get nervous about the financial health of their banks for the first time in generations, he said. Whalen's firm analyzes the safety and soundness of banks for business clients, but began receiving inquiries from individuals in the past two months for the first time, he said.

"If we don't get ahead of this, we are going to face a run on the retail banks by election day," he said.

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AP Business Writers Madlen Read, Tim Paradis and Stephen Bernard in New York, Martin Crutsinger in Washington, Ieva Augstums in Charlotte and Michael Liedtke in San Francisco contributed to this report.

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